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Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -03001=======================
2Kernel Probes (Kprobes)
3=======================
Jim Kenistond27a4dd2005-08-04 12:53:35 -07004
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -03005:Author: Jim Keniston <jkenisto@us.ibm.com>
6:Author: Prasanna S Panchamukhi <prasanna.panchamukhi@gmail.com>
7:Author: Masami Hiramatsu <mhiramat@redhat.com>
Jim Kenistond27a4dd2005-08-04 12:53:35 -07008
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -03009.. CONTENTS
Jim Kenistond27a4dd2005-08-04 12:53:35 -070010
Masami Hiramatsu9b173742017-10-06 08:16:37 +090011 1. Concepts: Kprobes, and Return Probes
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -030012 2. Architectures Supported
13 3. Configuring Kprobes
14 4. API Reference
15 5. Kprobes Features and Limitations
16 6. Probe Overhead
17 7. TODO
18 8. Kprobes Example
Masami Hiramatsu9b173742017-10-06 08:16:37 +090019 9. Kretprobes Example
20 10. Deprecated Features
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -030021 Appendix A: The kprobes debugfs interface
22 Appendix B: The kprobes sysctl interface
Naveen N. Rao0c75f122020-07-21 17:18:21 +053023 Appendix C: References
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -030024
Masami Hiramatsu9b173742017-10-06 08:16:37 +090025Concepts: Kprobes and Return Probes
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -030026=========================================
Jim Kenistond27a4dd2005-08-04 12:53:35 -070027
28Kprobes enables you to dynamically break into any kernel routine and
29collect debugging and performance information non-disruptively. You
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -030030can trap at almost any kernel code address [1]_, specifying a handler
Jim Kenistond27a4dd2005-08-04 12:53:35 -070031routine to be invoked when the breakpoint is hit.
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -030032
33.. [1] some parts of the kernel code can not be trapped, see
34 :ref:`kprobes_blacklist`)
Jim Kenistond27a4dd2005-08-04 12:53:35 -070035
Masami Hiramatsu9b173742017-10-06 08:16:37 +090036There are currently two types of probes: kprobes, and kretprobes
37(also called return probes). A kprobe can be inserted on virtually
38any instruction in the kernel. A return probe fires when a specified
39function returns.
Jim Kenistond27a4dd2005-08-04 12:53:35 -070040
41In the typical case, Kprobes-based instrumentation is packaged as
42a kernel module. The module's init function installs ("registers")
43one or more probes, and the exit function unregisters them. A
44registration function such as register_kprobe() specifies where
45the probe is to be inserted and what handler is to be called when
46the probe is hit.
47
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -030048There are also ``register_/unregister_*probes()`` functions for batch
49registration/unregistration of a group of ``*probes``. These functions
Masami Hiramatsu3b0cb4c2008-04-28 02:14:30 -070050can speed up unregistration process when you have to unregister
51a lot of probes at once.
52
Masami Hiramatsub26486b2010-02-25 08:35:04 -050053The next four subsections explain how the different types of
54probes work and how jump optimization works. They explain certain
55things that you'll need to know in order to make the best use of
56Kprobes -- e.g., the difference between a pre_handler and
57a post_handler, and how to use the maxactive and nmissed fields of
58a kretprobe. But if you're in a hurry to start using Kprobes, you
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -030059can skip ahead to :ref:`kprobes_archs_supported`.
Jim Kenistond27a4dd2005-08-04 12:53:35 -070060
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -030061How Does a Kprobe Work?
62-----------------------
Jim Kenistond27a4dd2005-08-04 12:53:35 -070063
64When a kprobe is registered, Kprobes makes a copy of the probed
65instruction and replaces the first byte(s) of the probed instruction
66with a breakpoint instruction (e.g., int3 on i386 and x86_64).
67
68When a CPU hits the breakpoint instruction, a trap occurs, the CPU's
69registers are saved, and control passes to Kprobes via the
70notifier_call_chain mechanism. Kprobes executes the "pre_handler"
71associated with the kprobe, passing the handler the addresses of the
72kprobe struct and the saved registers.
73
74Next, Kprobes single-steps its copy of the probed instruction.
75(It would be simpler to single-step the actual instruction in place,
76but then Kprobes would have to temporarily remove the breakpoint
77instruction. This would open a small time window when another CPU
78could sail right past the probepoint.)
79
80After the instruction is single-stepped, Kprobes executes the
81"post_handler," if any, that is associated with the kprobe.
82Execution then continues with the instruction following the probepoint.
83
Masami Hiramatsudcce32d2018-06-20 01:16:46 +090084Changing Execution Path
85-----------------------
86
Masami Hiramatsu01bdee62018-06-22 15:07:40 +090087Since kprobes can probe into a running kernel code, it can change the
88register set, including instruction pointer. This operation requires
89maximum care, such as keeping the stack frame, recovering the execution
90path etc. Since it operates on a running kernel and needs deep knowledge
91of computer architecture and concurrent computing, you can easily shoot
92your foot.
Masami Hiramatsudcce32d2018-06-20 01:16:46 +090093
94If you change the instruction pointer (and set up other related
Masami Hiramatsu01bdee62018-06-22 15:07:40 +090095registers) in pre_handler, you must return !0 so that kprobes stops
96single stepping and just returns to the given address.
Masami Hiramatsudcce32d2018-06-20 01:16:46 +090097This also means post_handler should not be called anymore.
98
Masami Hiramatsu01bdee62018-06-22 15:07:40 +090099Note that this operation may be harder on some architectures which use
100TOC (Table of Contents) for function call, since you have to setup a new
101TOC for your function in your module, and recover the old one after
102returning from it.
Masami Hiramatsudcce32d2018-06-20 01:16:46 +0900103
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300104Return Probes
105-------------
Abhishek Sagarf47cd9b2008-02-06 01:38:22 -0800106
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300107How Does a Return Probe Work?
108^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700109
110When you call register_kretprobe(), Kprobes establishes a kprobe at
111the entry to the function. When the probed function is called and this
112probe is hit, Kprobes saves a copy of the return address, and replaces
113the return address with the address of a "trampoline." The trampoline
114is an arbitrary piece of code -- typically just a nop instruction.
115At boot time, Kprobes registers a kprobe at the trampoline.
116
117When the probed function executes its return instruction, control
118passes to the trampoline and that probe is hit. Kprobes' trampoline
Abhishek Sagarf47cd9b2008-02-06 01:38:22 -0800119handler calls the user-specified return handler associated with the
120kretprobe, then sets the saved instruction pointer to the saved return
121address, and that's where execution resumes upon return from the trap.
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700122
123While the probed function is executing, its return address is
124stored in an object of type kretprobe_instance. Before calling
125register_kretprobe(), the user sets the maxactive field of the
126kretprobe struct to specify how many instances of the specified
127function can be probed simultaneously. register_kretprobe()
128pre-allocates the indicated number of kretprobe_instance objects.
129
130For example, if the function is non-recursive and is called with a
131spinlock held, maxactive = 1 should be enough. If the function is
132non-recursive and can never relinquish the CPU (e.g., via a semaphore
133or preemption), NR_CPUS should be enough. If maxactive <= 0, it is
wuqiang3b7ddab2022-11-10 16:15:02 +0800134set to a default value: max(10, 2*NR_CPUS).
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700135
136It's not a disaster if you set maxactive too low; you'll just miss
137some probes. In the kretprobe struct, the nmissed field is set to
138zero when the return probe is registered, and is incremented every
139time the probed function is entered but there is no kretprobe_instance
140object available for establishing the return probe.
141
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300142Kretprobe entry-handler
143^^^^^^^^^^^^^^^^^^^^^^^
Abhishek Sagarf47cd9b2008-02-06 01:38:22 -0800144
145Kretprobes also provides an optional user-specified handler which runs
146on function entry. This handler is specified by setting the entry_handler
147field of the kretprobe struct. Whenever the kprobe placed by kretprobe at the
148function entry is hit, the user-defined entry_handler, if any, is invoked.
149If the entry_handler returns 0 (success) then a corresponding return handler
150is guaranteed to be called upon function return. If the entry_handler
151returns a non-zero error then Kprobes leaves the return address as is, and
152the kretprobe has no further effect for that particular function instance.
153
154Multiple entry and return handler invocations are matched using the unique
155kretprobe_instance object associated with them. Additionally, a user
156may also specify per return-instance private data to be part of each
157kretprobe_instance object. This is especially useful when sharing private
158data between corresponding user entry and return handlers. The size of each
159private data object can be specified at kretprobe registration time by
160setting the data_size field of the kretprobe struct. This data can be
161accessed through the data field of each kretprobe_instance object.
162
163In case probed function is entered but there is no kretprobe_instance
164object available, then in addition to incrementing the nmissed count,
165the user entry_handler invocation is also skipped.
166
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300167.. _kprobes_jump_optimization:
168
169How Does Jump Optimization Work?
170--------------------------------
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500171
Masami Hiramatsu5cc718b2010-03-15 13:00:54 -0400172If your kernel is built with CONFIG_OPTPROBES=y (currently this flag
173is automatically set 'y' on x86/x86-64, non-preemptive kernel) and
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500174the "debug.kprobes_optimization" kernel parameter is set to 1 (see
175sysctl(8)), Kprobes tries to reduce probe-hit overhead by using a jump
176instruction instead of a breakpoint instruction at each probepoint.
177
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300178Init a Kprobe
179^^^^^^^^^^^^^
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500180
181When a probe is registered, before attempting this optimization,
182Kprobes inserts an ordinary, breakpoint-based kprobe at the specified
183address. So, even if it's not possible to optimize this particular
184probepoint, there'll be a probe there.
185
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300186Safety Check
187^^^^^^^^^^^^
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500188
189Before optimizing a probe, Kprobes performs the following safety checks:
190
191- Kprobes verifies that the region that will be replaced by the jump
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300192 instruction (the "optimized region") lies entirely within one function.
193 (A jump instruction is multiple bytes, and so may overlay multiple
194 instructions.)
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500195
196- Kprobes analyzes the entire function and verifies that there is no
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300197 jump into the optimized region. Specifically:
198
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500199 - the function contains no indirect jump;
200 - the function contains no instruction that causes an exception (since
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300201 the fixup code triggered by the exception could jump back into the
202 optimized region -- Kprobes checks the exception tables to verify this);
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500203 - there is no near jump to the optimized region (other than to the first
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300204 byte).
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500205
206- For each instruction in the optimized region, Kprobes verifies that
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300207 the instruction can be executed out of line.
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500208
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300209Preparing Detour Buffer
210^^^^^^^^^^^^^^^^^^^^^^^
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500211
212Next, Kprobes prepares a "detour" buffer, which contains the following
213instruction sequence:
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300214
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500215- code to push the CPU's registers (emulating a breakpoint trap)
216- a call to the trampoline code which calls user's probe handlers.
217- code to restore registers
218- the instructions from the optimized region
219- a jump back to the original execution path.
220
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300221Pre-optimization
222^^^^^^^^^^^^^^^^
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500223
224After preparing the detour buffer, Kprobes verifies that none of the
225following situations exist:
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300226
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900227- The probe has a post_handler.
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500228- Other instructions in the optimized region are probed.
229- The probe is disabled.
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300230
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500231In any of the above cases, Kprobes won't start optimizing the probe.
232Since these are temporary situations, Kprobes tries to start
233optimizing it again if the situation is changed.
234
235If the kprobe can be optimized, Kprobes enqueues the kprobe to an
236optimizing list, and kicks the kprobe-optimizer workqueue to optimize
237it. If the to-be-optimized probepoint is hit before being optimized,
238Kprobes returns control to the original instruction path by setting
239the CPU's instruction pointer to the copied code in the detour buffer
240-- thus at least avoiding the single-step.
241
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300242Optimization
243^^^^^^^^^^^^
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500244
245The Kprobe-optimizer doesn't insert the jump instruction immediately;
Paul E. McKenney1755ece2019-01-09 14:50:29 -0800246rather, it calls synchronize_rcu() for safety first, because it's
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500247possible for a CPU to be interrupted in the middle of executing the
Paul E. McKenney1755ece2019-01-09 14:50:29 -0800248optimized region [3]_. As you know, synchronize_rcu() can ensure
249that all interruptions that were active when synchronize_rcu()
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500250was called are done, but only if CONFIG_PREEMPT=n. So, this version
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300251of kprobe optimization supports only kernels with CONFIG_PREEMPT=n [4]_.
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500252
253After that, the Kprobe-optimizer calls stop_machine() to replace
254the optimized region with a jump instruction to the detour buffer,
255using text_poke_smp().
256
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300257Unoptimization
258^^^^^^^^^^^^^^
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500259
260When an optimized kprobe is unregistered, disabled, or blocked by
261another kprobe, it will be unoptimized. If this happens before
262the optimization is complete, the kprobe is just dequeued from the
263optimized list. If the optimization has been done, the jump is
264replaced with the original code (except for an int3 breakpoint in
265the first byte) by using text_poke_smp().
266
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300267.. [3] Please imagine that the 2nd instruction is interrupted and then
268 the optimizer replaces the 2nd instruction with the jump *address*
269 while the interrupt handler is running. When the interrupt
270 returns to original address, there is no valid instruction,
271 and it causes an unexpected result.
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500272
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300273.. [4] This optimization-safety checking may be replaced with the
274 stop-machine method that ksplice uses for supporting a CONFIG_PREEMPT=y
275 kernel.
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500276
277NOTE for geeks:
278The jump optimization changes the kprobe's pre_handler behavior.
279Without optimization, the pre_handler can change the kernel's execution
280path by changing regs->ip and returning 1. However, when the probe
281is optimized, that modification is ignored. Thus, if you want to
282tweak the kernel's execution path, you need to suppress optimization,
283using one of the following techniques:
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300284
Masami Hiramatsu059053a2018-06-20 01:10:27 +0900285- Specify an empty function for the kprobe's post_handler.
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300286
287or
288
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500289- Execute 'sysctl -w debug.kprobes_optimization=n'
290
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300291.. _kprobes_blacklist:
292
293Blacklist
294---------
Masami Hiramatsu376e2422014-04-17 17:17:05 +0900295
296Kprobes can probe most of the kernel except itself. This means
297that there are some functions where kprobes cannot probe. Probing
298(trapping) such functions can cause a recursive trap (e.g. double
299fault) or the nested probe handler may never be called.
300Kprobes manages such functions as a blacklist.
301If you want to add a function into the blacklist, you just need
302to (1) include linux/kprobes.h and (2) use NOKPROBE_SYMBOL() macro
303to specify a blacklisted function.
304Kprobes checks the given probe address against the blacklist and
305rejects registering it, if the given address is in the blacklist.
306
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300307.. _kprobes_archs_supported:
308
309Architectures Supported
310=======================
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700311
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900312Kprobes and return probes are implemented on the following
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700313architectures:
314
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500315- i386 (Supports jump optimization)
316- x86_64 (AMD-64, EM64T) (Supports jump optimization)
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700317- ppc64
Jim Keniston8861da32006-02-14 13:53:06 -0800318- ia64 (Does not support probes on instruction slot1.)
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700319- sparc64 (Return probes not yet implemented.)
Nicolas Pitre5de865b2007-12-03 17:15:52 -0500320- arm
Kumar Galaf8279622008-06-26 02:01:37 -0500321- ppc
David Daney9bb4d9d2010-08-03 11:22:22 -0700322- mips
Heiko Carstens369e8c32014-08-27 07:51:05 +0200323- s390
Sven Schnelle376e5fd2019-04-09 19:30:29 +0200324- parisc
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700325
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300326Configuring Kprobes
327===================
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700328
329When configuring the kernel using make menuconfig/xconfig/oldconfig,
Tiezhu Yange94102e2022-09-16 17:55:06 +0800330ensure that CONFIG_KPROBES is set to "y", look for "Kprobes" under
331"General architecture-dependent options".
Jim Keniston8861da32006-02-14 13:53:06 -0800332
333So that you can load and unload Kprobes-based instrumentation modules,
334make sure "Loadable module support" (CONFIG_MODULES) and "Module
335unloading" (CONFIG_MODULE_UNLOAD) are set to "y".
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700336
Ananth N Mavinakayanahalli09b18202006-10-02 02:17:32 -0700337Also make sure that CONFIG_KALLSYMS and perhaps even CONFIG_KALLSYMS_ALL
338are set to "y", since kallsyms_lookup_name() is used by the in-kernel
339kprobe address resolution code.
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700340
341If you need to insert a probe in the middle of a function, you may find
342it useful to "Compile the kernel with debug info" (CONFIG_DEBUG_INFO),
343so you can use "objdump -d -l vmlinux" to see the source-to-object
344code mapping.
345
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300346API Reference
347=============
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700348
349The Kprobes API includes a "register" function and an "unregister"
Masami Hiramatsu3b0cb4c2008-04-28 02:14:30 -0700350function for each type of probe. The API also includes "register_*probes"
351and "unregister_*probes" functions for (un)registering arrays of probes.
352Here are terse, mini-man-page specifications for these functions and
353the associated probe handlers that you'll write. See the files in the
354samples/kprobes/ sub-directory for examples.
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700355
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300356register_kprobe
357---------------
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700358
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300359::
360
361 #include <linux/kprobes.h>
362 int register_kprobe(struct kprobe *kp);
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700363
Peter Zijlstraec6aba32021-05-25 09:25:19 +0200364Sets a breakpoint at the address kp->addr. When the breakpoint is hit, Kprobes
365calls kp->pre_handler. After the probed instruction is single-stepped, Kprobe
366calls kp->post_handler. Any or all handlers can be NULL. If kp->flags is set
367KPROBE_FLAG_DISABLED, that kp will be registered but disabled, so, its handlers
368aren't hit until calling enable_kprobe(kp).
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700369
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300370.. note::
371
372 1. With the introduction of the "symbol_name" field to struct kprobe,
373 the probepoint address resolution will now be taken care of by the kernel.
374 The following will now work::
Ananth N Mavinakayanahalli09b18202006-10-02 02:17:32 -0700375
376 kp.symbol_name = "symbol_name";
377
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300378 (64-bit powerpc intricacies such as function descriptors are handled
379 transparently)
Ananth N Mavinakayanahalli09b18202006-10-02 02:17:32 -0700380
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300381 2. Use the "offset" field of struct kprobe if the offset into the symbol
382 to install a probepoint is known. This field is used to calculate the
383 probepoint.
Ananth N Mavinakayanahalli09b18202006-10-02 02:17:32 -0700384
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300385 3. Specify either the kprobe "symbol_name" OR the "addr". If both are
386 specified, kprobe registration will fail with -EINVAL.
Ananth N Mavinakayanahalli09b18202006-10-02 02:17:32 -0700387
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300388 4. With CISC architectures (such as i386 and x86_64), the kprobes code
389 does not validate if the kprobe.addr is at an instruction boundary.
390 Use "offset" with caution.
Ananth N Mavinakayanahalli09b18202006-10-02 02:17:32 -0700391
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700392register_kprobe() returns 0 on success, or a negative errno otherwise.
393
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300394User's pre-handler (kp->pre_handler)::
395
396 #include <linux/kprobes.h>
397 #include <linux/ptrace.h>
398 int pre_handler(struct kprobe *p, struct pt_regs *regs);
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700399
400Called with p pointing to the kprobe associated with the breakpoint,
401and regs pointing to the struct containing the registers saved when
402the breakpoint was hit. Return 0 here unless you're a Kprobes geek.
403
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300404User's post-handler (kp->post_handler)::
405
406 #include <linux/kprobes.h>
407 #include <linux/ptrace.h>
408 void post_handler(struct kprobe *p, struct pt_regs *regs,
409 unsigned long flags);
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700410
411p and regs are as described for the pre_handler. flags always seems
412to be zero.
413
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300414register_kretprobe
415------------------
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700416
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300417::
418
419 #include <linux/kprobes.h>
420 int register_kretprobe(struct kretprobe *rp);
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700421
422Establishes a return probe for the function whose address is
423rp->kp.addr. When that function returns, Kprobes calls rp->handler.
424You must set rp->maxactive appropriately before you call
425register_kretprobe(); see "How Does a Return Probe Work?" for details.
426
427register_kretprobe() returns 0 on success, or a negative errno
428otherwise.
429
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300430User's return-probe handler (rp->handler)::
431
432 #include <linux/kprobes.h>
433 #include <linux/ptrace.h>
434 int kretprobe_handler(struct kretprobe_instance *ri,
435 struct pt_regs *regs);
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700436
437regs is as described for kprobe.pre_handler. ri points to the
438kretprobe_instance object, of which the following fields may be
439of interest:
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300440
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700441- ret_addr: the return address
442- rp: points to the corresponding kretprobe object
443- task: points to the corresponding task struct
Abhishek Sagarf47cd9b2008-02-06 01:38:22 -0800444- data: points to per return-instance private data; see "Kretprobe
445 entry-handler" for details.
Ananth N Mavinakayanahalli09b18202006-10-02 02:17:32 -0700446
447The regs_return_value(regs) macro provides a simple abstraction to
448extract the return value from the appropriate register as defined by
449the architecture's ABI.
450
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700451The handler's return value is currently ignored.
452
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300453unregister_*probe
454------------------
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700455
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300456::
457
458 #include <linux/kprobes.h>
459 void unregister_kprobe(struct kprobe *kp);
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300460 void unregister_kretprobe(struct kretprobe *rp);
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700461
462Removes the specified probe. The unregister function can be called
463at any time after the probe has been registered.
464
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300465.. note::
Masami Hiramatsu3b0cb4c2008-04-28 02:14:30 -0700466
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300467 If the functions find an incorrect probe (ex. an unregistered probe),
468 they clear the addr field of the probe.
Masami Hiramatsu3b0cb4c2008-04-28 02:14:30 -0700469
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300470register_*probes
471----------------
472
473::
474
475 #include <linux/kprobes.h>
476 int register_kprobes(struct kprobe **kps, int num);
477 int register_kretprobes(struct kretprobe **rps, int num);
Masami Hiramatsu3b0cb4c2008-04-28 02:14:30 -0700478
479Registers each of the num probes in the specified array. If any
480error occurs during registration, all probes in the array, up to
481the bad probe, are safely unregistered before the register_*probes
482function returns.
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300483
Masami Hiramatsubc8c9da2018-06-20 01:04:38 +0900484- kps/rps: an array of pointers to ``*probe`` data structures
Masami Hiramatsu3b0cb4c2008-04-28 02:14:30 -0700485- num: the number of the array entries.
486
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300487.. note::
Masami Hiramatsu3b0cb4c2008-04-28 02:14:30 -0700488
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300489 You have to allocate(or define) an array of pointers and set all
490 of the array entries before using these functions.
Masami Hiramatsu3b0cb4c2008-04-28 02:14:30 -0700491
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300492unregister_*probes
493------------------
494
495::
496
497 #include <linux/kprobes.h>
498 void unregister_kprobes(struct kprobe **kps, int num);
499 void unregister_kretprobes(struct kretprobe **rps, int num);
Masami Hiramatsu3b0cb4c2008-04-28 02:14:30 -0700500
501Removes each of the num probes in the specified array at once.
502
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300503.. note::
Masami Hiramatsu3b0cb4c2008-04-28 02:14:30 -0700504
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300505 If the functions find some incorrect probes (ex. unregistered
506 probes) in the specified array, they clear the addr field of those
507 incorrect probes. However, other probes in the array are
508 unregistered correctly.
Masami Hiramatsude5bd882009-04-06 19:01:02 -0700509
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300510disable_*probe
511--------------
Masami Hiramatsude5bd882009-04-06 19:01:02 -0700512
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300513::
514
515 #include <linux/kprobes.h>
516 int disable_kprobe(struct kprobe *kp);
517 int disable_kretprobe(struct kretprobe *rp);
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300518
519Temporarily disables the specified ``*probe``. You can enable it again by using
Masami Hiramatsu8f9b1522009-04-06 19:01:02 -0700520enable_*probe(). You must specify the probe which has been registered.
Masami Hiramatsude5bd882009-04-06 19:01:02 -0700521
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300522enable_*probe
523-------------
Masami Hiramatsude5bd882009-04-06 19:01:02 -0700524
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300525::
Masami Hiramatsude5bd882009-04-06 19:01:02 -0700526
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300527 #include <linux/kprobes.h>
528 int enable_kprobe(struct kprobe *kp);
529 int enable_kretprobe(struct kretprobe *rp);
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300530
531Enables ``*probe`` which has been disabled by disable_*probe(). You must specify
Masami Hiramatsu8f9b1522009-04-06 19:01:02 -0700532the probe which has been registered.
Masami Hiramatsude5bd882009-04-06 19:01:02 -0700533
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300534Kprobes Features and Limitations
535================================
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700536
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900537Kprobes allows multiple probes at the same address. Also,
538a probepoint for which there is a post_handler cannot be optimized.
539So if you install a kprobe with a post_handler, at an optimized
540probepoint, the probepoint will be unoptimized automatically.
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700541
542In general, you can install a probe anywhere in the kernel.
543In particular, you can probe interrupt handlers. Known exceptions
544are discussed in this section.
545
Jim Keniston8861da32006-02-14 13:53:06 -0800546The register_*probe functions will return -EINVAL if you attempt
547to install a probe in the code that implements Kprobes (mostly
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300548kernel/kprobes.c and ``arch/*/kernel/kprobes.c``, but also functions such
Jim Keniston8861da32006-02-14 13:53:06 -0800549as do_page_fault and notifier_call_chain).
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700550
551If you install a probe in an inline-able function, Kprobes makes
552no attempt to chase down all inline instances of the function and
553install probes there. gcc may inline a function without being asked,
554so keep this in mind if you're not seeing the probe hits you expect.
555
556A probe handler can modify the environment of the probed function
557-- e.g., by modifying kernel data structures, or by modifying the
558contents of the pt_regs struct (which are restored to the registers
559upon return from the breakpoint). So Kprobes can be used, for example,
560to install a bug fix or to inject faults for testing. Kprobes, of
561course, has no way to distinguish the deliberately injected faults
562from the accidental ones. Don't drink and probe.
563
564Kprobes makes no attempt to prevent probe handlers from stepping on
565each other -- e.g., probing printk() and then calling printk() from a
Jim Keniston8861da32006-02-14 13:53:06 -0800566probe handler. If a probe handler hits a probe, that second probe's
567handlers won't be run in that instance, and the kprobe.nmissed member
568of the second probe will be incremented.
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700569
Jim Keniston8861da32006-02-14 13:53:06 -0800570As of Linux v2.6.15-rc1, multiple handlers (or multiple instances of
571the same handler) may run concurrently on different CPUs.
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700572
Jim Keniston8861da32006-02-14 13:53:06 -0800573Kprobes does not use mutexes or allocate memory except during
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700574registration and unregistration.
575
Masami Hiramatsu2bbda762018-06-20 01:16:17 +0900576Probe handlers are run with preemption disabled or interrupt disabled,
577which depends on the architecture and optimization state. (e.g.,
578kretprobe handlers and optimized kprobe handlers run without interrupt
579disabled on x86/x86-64). In any case, your handler should not yield
580the CPU (e.g., by attempting to acquire a semaphore, or waiting I/O).
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700581
582Since a return probe is implemented by replacing the return
583address with the trampoline's address, stack backtraces and calls
584to __builtin_return_address() will typically yield the trampoline's
585address instead of the real return address for kretprobed functions.
586(As far as we can tell, __builtin_return_address() is used only
587for instrumentation and error reporting.)
588
Jim Keniston8861da32006-02-14 13:53:06 -0800589If the number of times a function is called does not match the number
590of times it returns, registering a return probe on that function may
Ananth N Mavinakayanahallibf8f6e5b2007-05-08 00:34:16 -0700591produce undesirable results. In such a case, a line:
592kretprobe BUG!: Processing kretprobe d000000000041aa8 @ c00000000004f48c
593gets printed. With this information, one will be able to correlate the
594exact instance of the kretprobe that caused the problem. We have the
595do_exit() case covered. do_execve() and do_fork() are not an issue.
596We're unaware of other specific cases where this could be a problem.
Jim Keniston8861da32006-02-14 13:53:06 -0800597
598If, upon entry to or exit from a function, the CPU is running on
599a stack other than that of the current task, registering a return
600probe on that function may produce undesirable results. For this
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900601reason, Kprobes doesn't support return probes (or kprobes)
Jim Keniston8861da32006-02-14 13:53:06 -0800602on the x86_64 version of __switch_to(); the registration functions
603return -EINVAL.
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700604
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500605On x86/x86-64, since the Jump Optimization of Kprobes modifies
606instructions widely, there are some limitations to optimization. To
607explain it, we introduce some terminology. Imagine a 3-instruction
608sequence consisting of a two 2-byte instructions and one 3-byte
609instruction.
610
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300611::
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500612
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300613 IA
614 |
615 [-2][-1][0][1][2][3][4][5][6][7]
616 [ins1][ins2][ ins3 ]
617 [<- DCR ->]
618 [<- JTPR ->]
619
620 ins1: 1st Instruction
621 ins2: 2nd Instruction
622 ins3: 3rd Instruction
623 IA: Insertion Address
624 JTPR: Jump Target Prohibition Region
625 DCR: Detoured Code Region
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500626
627The instructions in DCR are copied to the out-of-line buffer
628of the kprobe, because the bytes in DCR are replaced by
629a 5-byte jump instruction. So there are several limitations.
630
631a) The instructions in DCR must be relocatable.
632b) The instructions in DCR must not include a call instruction.
633c) JTPR must not be targeted by any jump or call instruction.
Uwe Kleine-Königb5950762010-11-01 15:38:34 -0400634d) DCR must not straddle the border between functions.
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500635
636Anyway, these limitations are checked by the in-kernel instruction
637decoder, so you don't need to worry about that.
638
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300639Probe Overhead
640==============
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700641
642On a typical CPU in use in 2005, a kprobe hit takes 0.5 to 1.0
643microseconds to process. Specifically, a benchmark that hits the same
644probepoint repeatedly, firing a simple handler each time, reports 1-2
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900645million hits per second, depending on the architecture. A return-probe
646hit typically takes 50-75% longer than a kprobe hit.
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700647When you have a return probe set on a function, adding a kprobe at
648the entry to that function adds essentially no overhead.
649
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300650Here are sample overhead figures (in usec) for different architectures::
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700651
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900652 k = kprobe; r = return probe; kr = kprobe + return probe
653 on same function
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700654
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300655 i386: Intel Pentium M, 1495 MHz, 2957.31 bogomips
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900656 k = 0.57 usec; r = 0.92; kr = 0.99
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700657
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300658 x86_64: AMD Opteron 246, 1994 MHz, 3971.48 bogomips
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900659 k = 0.49 usec; r = 0.80; kr = 0.82
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700660
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300661 ppc64: POWER5 (gr), 1656 MHz (SMT disabled, 1 virtual CPU per physical CPU)
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900662 k = 0.77 usec; r = 1.26; kr = 1.45
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300663
664Optimized Probe Overhead
665------------------------
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500666
667Typically, an optimized kprobe hit takes 0.07 to 0.1 microseconds to
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300668process. Here are sample overhead figures (in usec) for x86 architectures::
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500669
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300670 k = unoptimized kprobe, b = boosted (single-step skipped), o = optimized kprobe,
671 r = unoptimized kretprobe, rb = boosted kretprobe, ro = optimized kretprobe.
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500672
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300673 i386: Intel(R) Xeon(R) E5410, 2.33GHz, 4656.90 bogomips
674 k = 0.80 usec; b = 0.33; o = 0.05; r = 1.10; rb = 0.61; ro = 0.33
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500675
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300676 x86-64: Intel(R) Xeon(R) E5410, 2.33GHz, 4656.90 bogomips
677 k = 0.99 usec; b = 0.43; o = 0.06; r = 1.24; rb = 0.68; ro = 0.30
678
679TODO
680====
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700681
Jim Keniston8861da32006-02-14 13:53:06 -0800682a. SystemTap (http://sourceware.org/systemtap): Provides a simplified
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300683 programming interface for probe-based instrumentation. Try it out.
Jim Keniston8861da32006-02-14 13:53:06 -0800684b. Kernel return probes for sparc64.
685c. Support for other architectures.
686d. User-space probes.
687e. Watchpoint probes (which fire on data references).
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700688
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300689Kprobes Example
690===============
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700691
Ananth N Mavinakayanahalli804defe2008-03-04 14:28:38 -0800692See samples/kprobes/kprobe_example.c
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700693
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300694Kretprobes Example
695==================
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700696
Ananth N Mavinakayanahalli804defe2008-03-04 14:28:38 -0800697See samples/kprobes/kretprobe_example.c
Jim Kenistond27a4dd2005-08-04 12:53:35 -0700698
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900699Deprecated Features
700===================
701
702Jprobes is now a deprecated feature. People who are depending on it should
703migrate to other tracing features or use older kernels. Please consider to
704migrate your tool to one of the following options:
705
706- Use trace-event to trace target function with arguments.
707
708 trace-event is a low-overhead (and almost no visible overhead if it
709 is off) statically defined event interface. You can define new events
710 and trace it via ftrace or any other tracing tools.
711
712 See the following urls:
713
714 - https://lwn.net/Articles/379903/
715 - https://lwn.net/Articles/381064/
716 - https://lwn.net/Articles/383362/
717
718- Use ftrace dynamic events (kprobe event) with perf-probe.
719
720 If you build your kernel with debug info (CONFIG_DEBUG_INFO=y), you can
721 find which register/stack is assigned to which local variable or arguments
722 by using perf-probe and set up new event to trace it.
723
724 See following documents:
725
Mauro Carvalho Chehab5fb94e92018-05-08 15:14:57 -0300726 - Documentation/trace/kprobetrace.rst
727 - Documentation/trace/events.rst
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900728 - tools/perf/Documentation/perf-probe.txt
729
Ananth N Mavinakayanahallibf8f6e5b2007-05-08 00:34:16 -0700730
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300731The kprobes debugfs interface
732=============================
733
Ananth N Mavinakayanahallibf8f6e5b2007-05-08 00:34:16 -0700734
735With recent kernels (> 2.6.20) the list of registered kprobes is visible
GeunSik Lim156f5a72009-06-02 15:01:37 +0900736under the /sys/kernel/debug/kprobes/ directory (assuming debugfs is mounted at //sys/kernel/debug).
Ananth N Mavinakayanahallibf8f6e5b2007-05-08 00:34:16 -0700737
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300738/sys/kernel/debug/kprobes/list: Lists all registered probes on the system::
Ananth N Mavinakayanahallibf8f6e5b2007-05-08 00:34:16 -0700739
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300740 c015d71a k vfs_read+0x0
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300741 c03dedc5 r tcp_v4_rcv+0x0
Ananth N Mavinakayanahallibf8f6e5b2007-05-08 00:34:16 -0700742
743The first column provides the kernel address where the probe is inserted.
Masami Hiramatsu9b173742017-10-06 08:16:37 +0900744The second column identifies the type of probe (k - kprobe and r - kretprobe)
745while the third column specifies the symbol+offset of the probe.
746If the probed function belongs to a module, the module name is also
747specified. Following columns show probe status. If the probe is on
Masami Hiramatsue8386a02009-01-06 14:41:52 -0800748a virtual address that is no longer valid (module init sections, module
749virtual addresses that correspond to modules that've been unloaded),
Masami Hiramatsude5bd882009-04-06 19:01:02 -0700750such probes are marked with [GONE]. If the probe is temporarily disabled,
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500751such probes are marked with [DISABLED]. If the probe is optimized, it is
Wang Long9ed330d2015-02-04 09:43:58 +0000752marked with [OPTIMIZED]. If the probe is ftrace-based, it is marked with
753[FTRACE].
Ananth N Mavinakayanahallibf8f6e5b2007-05-08 00:34:16 -0700754
GeunSik Lim156f5a72009-06-02 15:01:37 +0900755/sys/kernel/debug/kprobes/enabled: Turn kprobes ON/OFF forcibly.
Ananth N Mavinakayanahallibf8f6e5b2007-05-08 00:34:16 -0700756
Masami Hiramatsude5bd882009-04-06 19:01:02 -0700757Provides a knob to globally and forcibly turn registered kprobes ON or OFF.
758By default, all kprobes are enabled. By echoing "0" to this file, all
759registered probes will be disarmed, till such time a "1" is echoed to this
760file. Note that this knob just disarms and arms all kprobes and doesn't
761change each probe's disabling state. This means that disabled kprobes (marked
762[DISABLED]) will be not enabled if you turn ON all kprobes by this knob.
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500763
764
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300765The kprobes sysctl interface
766============================
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500767
768/proc/sys/debug/kprobes-optimization: Turn kprobes optimization ON/OFF.
769
770When CONFIG_OPTPROBES=y, this sysctl interface appears and it provides
771a knob to globally and forcibly turn jump optimization (see section
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300772:ref:`kprobes_jump_optimization`) ON or OFF. By default, jump optimization
773is allowed (ON). If you echo "0" to this file or set
774"debug.kprobes_optimization" to 0 via sysctl, all optimized probes will be
775unoptimized, and any new probes registered after that will not be optimized.
Mauro Carvalho Chehab43e5f7e2017-07-12 10:03:09 -0300776
777Note that this knob *changes* the optimized state. This means that optimized
Mauro Carvalho Chehaba1dac762017-05-14 16:51:34 -0300778probes (marked [OPTIMIZED]) will be unoptimized ([OPTIMIZED] tag will be
Masami Hiramatsub26486b2010-02-25 08:35:04 -0500779removed). If the knob is turned on, they will be optimized again.
780
Naveen N. Rao0c75f122020-07-21 17:18:21 +0530781References
782==========
783
784For additional information on Kprobes, refer to the following URLs:
785
Tiezhu Yang438697a2021-10-26 09:51:29 +0800786- https://lwn.net/Articles/132196/
Naveen N. Rao0c75f122020-07-21 17:18:21 +0530787- https://www.kernel.org/doc/ols/2006/ols2006v2-pages-109-124.pdf
788